Silicone hydrogel contact lenses have become popular due to the ability of contact lens wearers to wear such lenses on their eyes for longer times compared to non-silicone hydrogel contact lenses. Benefits to lens wearers associated with silicone hydrogel contact lenses can be attributed, at least in part, to the combination of hydrophilic components and the hydrophobic properties of silicone-containing polymeric materials of the contact lenses.
Non-silicone hydrogel contact lenses, such as 2-hydroxyethylmethacrylate (HEMA)-based contact lenses, are often produced in non-polar resin contact lens molds. In other words, lens precursor compositions for non-silicone hydrogel contact lenses are polymerized in non-polar resin contact lens molds to produce polymeric lenses. A contact lens mold typically includes a female mold member and a male mold member, which can be assembled together by an interference type of engagement or other forms of engagement to form a contact lens mold having a contact lens shaped cavity. Non-polar resins, such as polypropylene and polystyrene, are useful in producing such molds since the plastic mold members are easily separated and are deformable to facilitate the engagement and separation of the mold members.
However, existing silicone hydrogel contact lenses produced using non-polar resin molds may have hydrophobic lens surfaces. In other words, the surfaces of such silicone hydrogel contact lenses have low wettability and therefore are not ophthalmically compatible. Surface treatments or surface modifications have been used on the surfaces of such silicone hydrogel contact lenses to increase the hydrophilicity and wettability of the lens surfaces. One approach involves treating the surface of the polymerized lens, for example using plasma techniques, to increase its hydrophilicity of the lens surface. Another approach involves derivatizing the hydrogel monomer mix during polymerization using reactive hydrophilic moieties to confer a hydrophilic surface after the lens has been formed. Surface treatment of contact lenses requires increased machinery and time to produce contact lenses compared to manufacturing methods that do not use surface treatments or modifications.
As an alternative to surface treatment, it has been found that silicone hydrogel contact lenses with ophthalmically acceptable surface wettabilities can be produced using polar resin molds instead of non-polar resin molds. For example, silicone hydrogel contact lenses formed in ethylenevinyl alcohol or polyvinyl alcohol based molds have desirable surface wettabilities. One example of a useful polar resin used in the manufacture of silicone hydrogel contact lenses is a resin of ethylene-vinyl alcohol copolymers such as the ethylene-vinyl alcohol copolymer resin sold under the trade name Soarlite™ by Nippon Gohsei, Ltd. In addition to its polarity, Soarlite™ is said to have the following preferred characteristics: extremely high mechanical strength, antistatic properties, low contractility when used in molding processes, excellent oil and solvent resistance, small coefficient of thermal expansion, and good abrasion resistance.
Although polar resins provide a desirable alternative for producing silicone hydrogel contact lenses, polar resin molds are less deformable or flexible than non-polar resin molds, and are relatively more difficult to work with. Therefore, alternative forms of securing polar resin mold members together may be used. For example, male and female polar resin mold members may be welded together to form a contact lens mold having a lens shaped cavity. During the production of silicone hydrogel contact lenses, it is necessary to separate the male and female polar resin mold members to reveal the polymerized silicone hydrogel lens product. The separation of the polar resin mold members is difficult and can present challenges to the automation and throughput of large numbers of such contact lenses. For example, separation of polar resin mold members may require the use of ultrasonic energy, applying a temperature differential across the contact lens mold, contacting the contact lens mold with a heated liquid, separating the mold members using wedging instruments, and the like. Not only can the demolding of the male and female mold members be difficult, but the delensing or deblocking of the polymerized lens from a mold member without damaging the lens can be difficult to achieve. While not wishing to be limited by theory in any way, this difficulty may be caused at least in part by electrostatic interactions, dipole-dipole interactions, ion-dipole interactions, hydrogen bonding, and Van der Walls forces between the polymerized lens and the mold halves.
Examples of documents which may relate to the production of contact lenses, such as silicone hydrogel contact lenses, include U.S. Pat. Nos. 4,121,896; 4,495,313; 4,565,348; 4,640,489; 4,889,664; 4,985,186; 5,039,459; 5,080,839; 5,094,609; 5,607,518; 5,850,107; 5,935,492; 6,867,245; 6,869,549; 6,939,487; and U.S. Patent Publication No. 20050154080.
In sum, an existing problem relates to the difficulty of separating polar resin mold members used in the production of silicone hydrogel products, such as silicone hydrogel contact lenses. In view of the above, there remains a need for new and improved ways in which to separate polar resin mold members used in the production of silicone hydrogel products or devices with desirable properties, such as silicone hydrogel contact lenses with ophthalmically acceptable properties, including desirable surface wettabilities and the like. The current invention meets this need, among others.